On the calculation of the pressure drag coefficient of a flat plate using the law of conservation of energy

The article is concerned with the development of a new physical model for calculating the pressure resistance of a normally oriented thin flat plate moving in incompressible non-viscous fluid. Only two fundamental assumptions are used – the law of conservation of energy and the continuity condition. The main idea is to represent the motion of the plate as a sequence of discrete steps so that to calculate the increment of the kinetic energy of fluid particles both before and after the plate at each step. An important feature is a separate estimation of the pressure resistance of the front and back surfaces of the plate. It proved that the coefficient of pressure drag for the front side equals to 1.0, for the back side it is 0.33 for a linear approximation of the velocity profile of fluid particles near the surface, and 0.20 for a quadratic approximation. So the total drag coefficient can be in the interval 1.20–1.33 that is very close to published experimental data. In the case of arbitrary oriented plate, an effect of lateral flows from adjacent plates takes place. This effect has been studied and applied to calculate the pressure drag of a circular cylinder, as well as to computing the pressure drag of the hull of a real vessel.